On dewetting dynamics of solid films of hydrogen isotopes and its influence on tritium ß spectroscopy

The dewetting dynamics of solid films of hydrogen isotopes, quench-condensed on a graphite substrate, was measured at various temperatures below desorption by observing the stray light from the film. A schematic model describing the dewetting process by surface diffusion is presented, which agrees qualitatively with our data. The activation energies of different hydrogen isotopes for surface diffusion were determined. The time constant for dewetting of a quench-condensed film at the working temperature of 1.86 K of the mainz neutrino mass experiment was extrapolated. Received 30 December 1999     

Cooperativity in a spin transition ferrous polymer: Interacting domain model, thermodynamic, optical and EPR study

A new thermodynamic model is proposed in order to account for the high spin low spin conversion in metal-organic polymers. The model, based on the idea that the spin conversion occurs in interacting domains of like-spin metal ions, allows to explain most of the important features of various types of spin conversion. The sine qua non condition of the existence of spin transitions with hysteresis is obtained. In the case of very large cooperativity, the model predicts unusual behaviour of the spin conversion system due to a low-temperature metastable high spin state. Existence of such a state is interesting in the context of the light induced excited spin state trapping recently observed in some ferrous compounds. The model is applied to interpret the spin transition in polycrystalline ferrous polymer [Fe _1-y Cu _y (Htrz)₂ trz] (BF ₄) with y = 0.00, 0.01 and 0.10, detected by differential scanning calorimetry, optical reflectivity and electron paramagnetic resonance. The domain size and the interaction energy between the domains are estimated as, respectively, n = 11 and for the y = 0 compound. As the copper content is growing, n and tend to decrease, resulting in transformations of the shape of hysteresis loop which becomes less steep, narrows and shifts to lower temperatures. The electron paramagnetic resonance gives further evidence of the presence of like-spin domains. Received 27 November 1998 and Received in final form 19 April 1999     

钢中小角度晶界区的电子结构及掺杂效应

根据位错的弹性理论,建立了9Ni钢中53°掺杂小角度晶界的原子模型,利用Recursion方法,计算了杂质在53°小角度晶界典型环境中的能量和电子结构,由此得出,钢中小角度晶界的强度敏感地依赖于隔离杂质的类型,S,P杂质使晶粒间结合减弱,从而导致晶界疏松 ;相反,B,C,N则会使晶界间的结合加强.在所有的杂质中,B显示出独特的性质,在钢中B 不仅能增强晶界的结合,而且由于占位竞争效应会使其他杂质远离晶界,具有净化晶界的作用. 关键词： 小角晶界 杂质 占位竞争 晶界隔离     

Semiempirical calculations on WO3 and MXWO3 crystals (M = H,Li, Na)

The monoclinic structure of tungsten trioxide WO₃ has been studied by combining a modified intermediate neglect of differential overlap (INDO) method and the supercell model. The fitted semiempirical parameters describe very well the features of the band structure and crystal structure. Calculations of H, Li, and Na impurities in a WO₃ crystal have been performed to study the absorption spectra and the equilibrium geometries of intercalated impurities. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 729–735, 1997     

Binding energy of hydrogenic impurity states in an inverse parabolic quantum well under static external fields

In the present theoretical study, we investigate the influence of external fields (electric and/or magnetic) on the binding energy of hydrogenic impurities in a GaAs/Ga_1-xAl_xAs inverse parabolic quantum well, in which the parabolicity depends on the Al concentrations at the well center. Our calculations have been based on the potential morphing method in the effective mass approximation. The systematic theoretical investigation contains results with all possible combinations of the involved parameters, as quantum well width, Al concentrations at the well center, position of the impurity and magnitudes of the external fields.     

Sample stacking for determination of aromatic acid impurities by microemulsion electrokinetic chromatography

In this study, a sample stacking step coupled with microemulsion electrokinetic chromatography (MEEKC) was used to detect and analyze nine aromatic acids (benzoic acid (BA), isophthalic acid (IPA), terephthalic acid (TPA), p-toluic acid (p-TA), 4-carboxylbenzaldehyde (4-CBA), trimesic acid (TSA), trimellitic acid (TMA), o-phthalic acid (OPA), and hemimellitic acid (HMA)) which are common impurities produced during aromatic acid synthesis. First, the presence of both acid and water plugs at the front of the capillary improved the reproducibility in retention time and peak intensity of the tested analytes in the stacking method. Second, the pH and the electrolyte type of acidic plug and sample matrix were found to be the predominant influences on the aromatic acid stacking. The detection limits of these aromatic acids were reduced to the range of 0.00007-0.00032 μg mL⁻¹ by this optimal sample stacking step. This proposed on-line concentration MEEKC method was able to detect trace levels of aromatic acid impurities in commercial aromatic acid products that were not previously possible by the normal MEEKC method. Furthermore, these results in comparison with our previous studies on sample stacking MEEKC method indicated that all acidic species were concentrated by this simple stacking procedure. The sensitivity enhancement, however, was highly dependent on the types of functional groups present in the structures of analytes, and the enhancement was in the order of first the compounds carrying both carboxy and hydroxy groups (e.g. phenolic acid), followed by carboxylic acid compounds (e.g. aromatic acid), and then phenol compounds (e.g. polyphenol).     

Metallic Impurities within Residual Catalyst Metallic Nanoparticles Are in Some Cases Responsible for “Electrocatalytic” Effect of Carbon Nanotubes

It′s what′s on the inside that counts : In some cases, the metallic impurities within residual catalyst metallic nanoparticle impurities, which remain in carbon nanotubes even after their purification, are responsible for the “electrocatalytic” properties of carbon nanotubes. This is demonstrated by using double‐walled carbon nanotubes (DWCNTs) containing cobalt residual catalyst nanoparticle impurities, which themselves contain iron‐based impurities.

     

Local density of states around two nonmagnetic impurities in cuprate superconductors

The local density of states (LDOS) around two nonmagnetic impurities which are located at different sites is studied within the two-dimensional t-J-U model. The order parameters are determined in a self-consistent way with the Gutzwiller projected mean-field approximation and the Bogoliubov-de Gennes theory. When the two impurities are located one or two sites away, we find the superconductivity coherence peaks are more strongly suppressed and the zero-energy peak (ZEP) has split into two peaks. Whereas when the two impurities are located next to each other, the ZEP vanished, and LDOS does not change a lot compared with the case away from the impurities.     

磁场和量子点尺寸对方形杂质量子点中电子性质的影响

利用二维有限差分方法,计算了含有H_2~+杂质的方形量子点的基态能和杂质束缚能。讨论了磁场和杂质位置对不同尺寸的量子点中电子基态能量和束缚能的影响,得出了方形量子点系统的量子尺寸效应。     

Investigation of influential factors on the purification of zone‐refined germanium ingot

Zone refining is one of the most important procedures to purify germanium crystals for the fabrication of detectors in our laboratory. In order to properly zone refine high‐purity germanium crystals, it is important to develop perfect cleaning procedures for raw materials, quartz tubes, and the containers holding raw materials. Additionally, vacuum levels, container types, the correct combination of ambient gases, the speed of zone travel, and the ratio of ingot length to molten zone length, all need to be carefully studied in order to obtain the best results possible. In this work, we investigate a number of influential factors in perfecting high‐purity germanium crystal growth, specifically: cleaning procedures, boat composition, vacuum levels in the chamber, zone travel speed, and the ratio of ingot length to molten zone length. Using the van der Pauw Hall technique, we were able to measure the electrical properties of zone‐refined ingots and analyze the origin and distribution of three main impurity elements (boron, aluminum and phosphorus) thereby allowing us to study potential contamination sources. After detailed analysis on the various influential factors, we were able to optimize the zone‐refining procedures.